The initial plan was to pick an Evolution textbook with a nice timeline and use that. Evolution by Barton et al., for example, has nice timeline inside the front cover. The problem with this was that we could not find any credits or sources for the illustration. (It was also missing a few of the events from the original paper.) Looking at other books on our shelves lead to similar problems. We are not Deep Time experts and are not aiming to endorse certain dates or theories over others - we just want to provide a useful tool for the community.
In the end, we settled on The New Scientist evolution of life website because it not only covered many of the events from the MapTime paper but it also contains links out to articles - including, in many cases, the original literature. If you visit the site, you will notice that we haven't included all of the Time Points. There are rather a lot! If your favourite one is missing, let us know. For the more recent events that are not covered by this Timeline we have, for the moment, relied on Wikipedia and Google to "crowd source" the date.
We don't intend to stick exclusively with this Timeline forever, although we will keep the Time Points in the website. The planned developments for MapTime include the opportunity to add your own Time Point and Timelines. We would still like to maintain a scientifically accurate, and educationally useful, default timeline, though. We therefore welcome feedback and suggestions - not just in terms of the key events but also corrections to the accepted dates. We do ask for peer-reviewed citations for any requested additions/corrections, though.